2. Those people in their early twenties who work on school campuses and whose only purpose is to inform teachers when students have done something wrong. They are usually seen riding golf-carts, staring off into space, chatting it up on walking-talkies,and generally acting as if they have something important and relevent that they are doing when, in fact, they are completely useless.

1. Man, my sister is such a narc, she told our parents I snuck out of the house last night.

2. The stupid Narc almost ran me off the sidewalk and then had the nerve to yell at me because I was on the grass!

Narc is a shortened form of Narcotic and may refer to hard drugs or, by extension to a police officer from the drugs squad.

NB:
This word is often confused with nark. Nark is British and Australian slang for
(i) noun: a police informer, or more widely, anyone who reports illegal or anti-social activities to any authorities.
(ii) verb: to annoy, to irritate,

"See, that guy over there? The one who looks like a druggie? He's undercover, he's a narc."

"That guy just asked me for money for a cup of coffee"
"Cup of coffee? He's a junky, he wants his narcs."